Recently, thickness of display apparatuses such as liquid crystal displays and plasma displays has been reduced. Further, display apparatuses that have a large screen size have been prevailing.
Such a thin and large-screen display apparatus may be used, for example, in presentation in a meeting, presentation for introducing a product or the like, or as a display apparatus for a video game. In a scene in which the display apparatus is used in the above-mentioned way, the display apparatus is operated by pointing, with the use of an operating device such as a pointer, a desired point (position or place) on an image that is displayed on the display screen.
For example, Patent Document 1 (Japanese Unexamined Patent Publication No 66080/2007 (Tokukai 2007-66080) (published on Mar. 15, 2007)) discloses a technique for detecting coordinates of a pointed point on a display screen. In the technique, (i) light emitting devices provided to front and rear ends of a pointer are driven in different blinking patterns, respectively, (ii) images including light-emitting areas that are provided to the front and rear ends of the pointer are captured by cameras that are provided on the right and left sides of the display screen, respectively, and (iii) coordinates of a pointed point on the display screen is detected by analyzing/calculating, according to the trigonometry, a direction (angle) of each of the light-emitting areas and a distance between (a) each of the light-emitting areas and (b) each of the cameras or the display screen.
Patent Document 2 (Japanese Unexamined Patent Publication No. 83024/2007 (Tokukai 2007-83024) (published on Apr. 5, 2007)) discloses a system that detects a position of coordinates on a display screen. In the system, a module including an LED that emits infrared light is provided in the vicinity of the display screen, for example, at an upper part or a lower part of a display apparatus, (ii) an image of the LED is captured by using (a) a filter that is provided in a controller and transmits only infrared light and (b) an image sensing device such as a CMOS sensor or a CCD, and (iii) a position of coordinates in the display screen is detected from a positional change of the LED in data of thus captured image.
According to the conventional techniques, unfortunately, a position pointed by the operating device cannot be appropriately detected in a case where a position of the operating device is close to the display screen.
That is, in the technique as disclosed in Patent Document 1, the cameras for capturing images of the lightening points at the front and rear ends of the pointer (operating device) are provided on the left and right sides of the display screen in the display apparatus. As such, in a case where a position of the pointer is close to the display screen, the lightening point may be in a position out of a range in which the camera can capture an image.
As for the technique as disclosed in Patent Document 2, an image sensing device provided in a controller (operating device) is arranged to capture an image of the infrared light emitted by the LED module that is provided at an upper part or a lower part of the display screen of the display apparatus. Therefore, as in the case of Patent Document 1, in a case where a position of the controller is close to the display screen, the LED module may be in a position out of a range in which the image sensing device can capture an image.
FIGS. 25(a), 25(b), 26(a), and 26(b) are explanatory diagrams each illustrating a relation of (i) a distance between an operating device 101 and a display apparatus 102 and (ii) a range in which a position that is pointed by the operating device 101 can be detected, in the same arrangement as the arrangement disclosed in Patent Document 2.
FIGS. 25(a) and 25(b) illustrates a case where a distance between the display apparatus 102 and the operating device 101 is sufficiently large. In such a case, an LED module 103 is included within a range in which the image sensing device that is provided in the operating device 101 can capture an image, regardless of a position, on the display screen, that is pointed by the operating device 101. Therefore, in such a case, a position pointed by the operating device 101 can be detected.
On the other hand, FIGS. 26(a) and 26 (b) illustrates a case where the distance between the display apparatus 102 and the operating device 101 is short. In such a case, the LED module 103 cannot be within a range in which the image sensing device can capture an image, depending on a position pointed by the operating device 101. In this case, the position pointed by the operating device 101 cannot be detected.
In the conventional techniques explained above, when a position on the display screen is pointed by the operating device in a state where the operating device is rotated around an axis that is a linear line connecting between the operating device and the display screen (for example, in a sate where the operating device is turned upside down), the pointed position may not be detected properly. In other words, in a case where the operating device is rotated with respect to a reference position around an axis in an image capture direction (a direction in which the operating device captures an image), a wrong pointed position may be detected. The reference position here is assumed to be a position in which an x-axis direction and a y-axis direction in a coordinate system of the display screen agree with an x-axis direction and a y-axis direction in a coordinate system of a captured image, respectively.
For example, as illustrated in FIGS. 27(a) and 28(a), a case where the light-emitting areas L1 and L2 are provided on the right and left sides of the display screen, respectively, is considered. In a case where the operating device that is not turned upside down (in a state where the operating device is in the reference position) points a lower-left position of the display screen as illustrated in FIG. 27(a), a captured image becomes as illustrated in FIG. 27(b). On the other hand, the operating device that is turned upside down (in a state where the operating device is rotated with respect to the reference position around an axis in the image capture direction) points an upper-left position of the display screen as illustrated in FIG. 28(a), a captured image becomes as illustrated in FIG. 28(b). In this way, thought the operating device points different positions on the display screen, the same captured images are obtained in a case where the operating device is turned upside down and in a case the operating device is turned not upside down, respectively. As a result, the pointed position may be wrongly detected.